Lake-Effect Snow May Need Mountain Effects, Too

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Those who live around the Great Lakes are very familiar with the
snow those bodies of water can bring, a phenomenon called
lake-effect snow. But a new study suggests that lakesaren'talways
the only feature behind the falling flakes.

Nearby mountains can enhance or dampen a lake-effect storm,
depending on where they sit in relation to the lake, and they may
even be necessary to triggersome lake-effect snowfall, the study
finds.

University of Utah researchers explored the role that local
topography plays in driving
lake-effect snow with computer simulations of a lake-effect
storm around
Utah's Great Salt Lake, even with the relatively gentle
terrain around the lake.

"It is going to help us with
weather prediction — helping forecasters recognize that in
some lake-effect events, the mountains or hills can play an
important role in triggering lake-effect snow bands" over large
bodies of water,study author Jim Steenburgh said in a university
release.

Mountains' influence

Here's how the lake effect works: A cold air mass moves over a
large body of water that is warm in comparison (because more heat
has to be released to change the temperature of water than air);
the air picks up moisture and heat, then rises. As it does so,
the air cools, and the moisture it contains condenses out,
forming snow if the air is cold enough.

It was previously known that lake-effect snow could intensify as
it moved up over a mountain, which further cools the air and
forces more moisture out over the highlands. But the simulations
of lake-effect storms around the Great Salt Lake that Steenburgh
and his colleagues ran showed that sometimes the influence of the
mountains extended below the high mountain altitudes, triggering
snow over lowlands and the lake itself when the mountains were
downstream of the body of water. [ The
World's Weirdest Weather ]

In other cases, mountains upstream of the lakedampened the
lake-effect snow, because the cold air descending down the side
of the mountain warmed and dried before it hit the lake. This
resulted in less snow fall than if the mountains weren't present.

The configuration of mountains can also force together cold air
masses, making them converge over the lake.

"Most people recognize that mountains get more precipitation than
lowlands, because of moist air being lifted over the mountains,"
Steenburgh said in the release. "Everybody recognizes that it
plays a role in lake-effect storms. What we're showing here is a
situation where the terrain is complicated.There are multiple
mountain barriers, not just one, and they affect the air flow in
a way that influences the development of the lake-effect storm
over the lake and lowlands, rather than just over the mountains."

Missing from models

This unrecognized abilityof the mountains to both dampen and
trigger snow could help explain why forecasters have difficulty
predicting the occurrence of lake-effect storms and
how much snow they will drop on Utah's cities, Steenburgh
said. The models currently used don't adequately include the
Wasatch Range or the northern mountains along the
Nevada-Idaho-Utah border.

Gaininga better idea of the factorsinfluencing lake-effect snow
will help forecasters better predict the traffic snarls the
weathercan cause, as well as the fresh snow it can provide to ski
resorts.